1. Field of the Invention
The present invention relates to ultrasonic measurements of multiphase mixtures of oil, water and gas flowing in pipes or conduits, and particularly where the mixtures have a high presence or quantity of gas content in the flowing mixtures.
2. Description of the Related Art
Tomographic imaging of flow tends to focus in general on the imaging of two phases. The technique generally used for two phase flow reconstruction has been based upon what is known as the filtered back projection algorithm. This type of flow reconstruction is described for example by Kak, Avinash C., Slaney, Malcolm “Principles of Computerized Tomographic Imaging,” IEEE Press, New York, USA (1988), and Murrell, H. “Computer-Aided Tomography,” The Mathematical J. V6 (1996), pp. 60-65.
However, because of the nature of the fluids present in production of oil and gas it is necessary to form images of three phase flow in conduits involved in hydrocarbon production. Because of the different fluid properties of water (brine), oil and gas it is difficult to address all three sets of fluids simultaneously. In the case of oil-water or water-oil multiphase flows, the medium has been utilized. In the case of liquid-gas or gas-liquid flows (where the liquid is brine or oil or both) an attenuation approach has been utilized. As far as is known, neither method, however, has provided a wholly satisfactory measure or representation of a three phase multiphase flow cross section or of determined volume fractions of each of the three phases. This is particularly the case when there is a significant volume of gas phase in the flowing mixture.
As disclosed in commonly owned U.S. Pat. Nos. 9,424,674 and 9,404,781, flow measures and tomographic images of multiphase mixtures have been obtained when the multiphase mixture is in laminar flow at the location along the pipe where transducer arrays were located to obtain ultrasonic measurements from the multiphase mixture. For this reason, structures in the form of bluff bodies have been mounted in the pipe for the specific purpose of causing laminar flow to be present in the flowing fluid when the fluid passed through the ultrasonic transducers for the purposes of measurement. During laminar flow, the velocity, pressure, and other flow properties at each point in the fluid remain constant. The multiphase fluid during laminar flow moves in parallel layers, with no disruption between the layers. In laminar flow, the multiphase fluid tends to flow without lateral mixing the fluid moves through the pipe or conduit, with the upstream structure causing the fluid to flow substantially along that longitudinal axis. There is thus minimal flow of the multiphase fluid in directions or planes transverse the longitudinal axis of the pipe. Actual flow conditions of the multiphase fluid are, however, typically not those of laminar flow. Under actual flow conditions the formation of accurately indicative measures and indications of the flow conditions and flow rates of the various phases has proven difficult. This is particularly the case when there is fluid containing a significant percentage of gas, or in conditions when the gas flow is not uniformly distributed in the multiphase fixture.